Spine
Cervical spine, seven in total, lies between the skull and the thoracic vertebra. There is typical and atypical cervical vertebra. Structure of a typical cervical vertebra * The kidney shaped body is similar in size or smaller than the vertebral foramen. * The lateral edge of the body is projected up into a lip called uncus. * The pedicle is attached directly under the uncus * The transverse process is perforated by the foramen and lies immediately lateral to the vertebral body. The posterior bar of the bone that projects from the pedicle behind the foramen is the true transverse element. The bar of bone passing in front of the foramen and end at the anterior tubercle along with the intertubercle lamellae that joints this to the posterior tubercle is part of the costal element. * The anterior tubercles enlarge progressively from C3 to C6. The C6 anterior tubercle is the common carotid tubercle because the common carotid artery can be compressed against it. * The lamina encloses a relatively large triangular shaped vertebral foramen. * The superior articular facets face obliquely up and back and the inferior articular facets face down and forward. * Spinous process is short and bifid. * Intervertebral foramen is oriented anterolaterally below pedicles at approximately 45° to sagittal plane Structure of the transverse foramen * Each cervical vertebra has foramen in the transverse processes (foramen transversarium) and no costal facets like the thoracic vertebra. Costal elements that form the ribs in thoracic spine, fuses in the cervical spine to form the transverse foramen. * Prevertebral artery with its accompanying sympathetic nerve fibres and vertebral venous plexus lying within the foramen. Joints * Intervertebral disc ** Narrowest in cervical region ** Thinner posteriorly than anteriorly ** Do not extend to lateral margins of vertebral bodies in cervical spine → joints of Luschka * Uncovertebral joint (joints of Luschka) ** Oblique, cleft-like cavities between superior surfaces of uncinate processes & lateral lips of inferior articular surface of next superior vertebra ** Lined by cartilaginous endplate of vertebral body ** No true synovial lining present; contains serum, simulating synovial fluid * Facet (zygapophyseal) joints ** Facet joints oriented approximately 45° superiorly from transverse plane in upper cervical spine; assume more vertical orientation toward C7 ** Formed by articulation between superior & inferior articular processes = articular "pillars" which support the cranium as well Ligaments * Anterior & posterior longitudinal, ligamentum flavum, interspinous & supraspinous ligaments * Additional ligaments of CCJ include apical, alar, and cruciate ligaments The atlas The C1 vertebra is an atypical cervical vertebra and is the widest of the cervical vertebra. * Lacks a centrum and is modified to form thick lateral mass on each side. These transmit the weight of the skull immediately below. * Lateral mass joined at the front by a short anterior arch and a longer posterior arch at the back. . ** The short anterior arch is projected into a tubercle in front for attachment of the anterior longitudinal ligament. ** The longer posterior arch is grooved by the vertebral artery. * The lateral mass is projected into the transverse process, which is perforated by the foramen. There is no tubercle on the transverse process but the blunt end of the transverse process represents the attachment for the scalenus medius and levator scapulae. * The upper surface is kidney shaped and concave for articulation with the occipital condyle. The lower surface is round and almost flat for lateral atlantoaxial joint. The axis The C2 vertebra is another atypical cervical vertebra characterised by the dens and a large spinous process. * The dens projects upwards from the anterior arch and has articular facet at the front for the joint with the anterior arch of the atlas. It bears no weight. * The transverse process has no anterior and posterior tubercle but ends in a rounded tip. * An inferior articular process extends down from the junction of the pedicle and lamina It's articular facet face is downwards and forwards as in typical cervical vertebra. * The large spinous process ends in a wide bifurcation resembling an inverted U The C7 vertebrate Often called a the vertebral prominen because of its prominent spine. Unique features: * long spine (not bifid) * transverse processes, short and project inferolateally, compared with T1 spinous processes, which are long & project superolaterally * the foramen of the transverse process does not transmitted the vertebral artery. The foramen is small and contains posterior vein when vertebral vein is double. Ossification: * Atlas (C1) ** Two to five (3 most common) 1° ossification centers *** Anterior arch (1), posterior arch (1) + lateral masses (2) ** No 2° ossification centers * Axis (C2) ** Five 1° ossification centers *** Centrum (1), posterior vertebral neural arch (2), odontoid process (2) *** Dens separated from C2 centrum by remnant of embryonic C1-2 disc ** Two 2° ossification centers *** Inferior annular epiphysis, apex of odontoid * C3-6 ** Three 1° ossification centers per each vertebra *** Centrum (1), posterior vertebral neural arch (2) ** Five 2° ossification centers per each vertebra *** Spinous process apex (1), transverse process apex (2), annular epiphysis (2) * C7 ** Same 1°/2° ossification centers as C3-6 *** Plus 1° ossification centers for two costal processes *** These appear by 6 months of age *** Fuse with transverse process, vertebral body by 5-6 years *** If remain unfused → cervical ribs (1%) Anatomical variation: * atlanto-occipital fusio (partial or complete) * cervical rib * accessory ossicle of the anterior arch of the atlas * persistent ossiculum terminale in the axis * seasamoid ossicle of the nuchal ligament * C7 transmission of the vertebral artery * incomplete ossification of the anterior and posterior arch of atlas or agenesis * The dens of the axis may be: ** a separate bone, the os odontoideum; ** arise from the anterior arch ** articulate with a third occipital condyle ** be absent. * Pseudosubluxation of C2/C3 Cervical rib: Cervical rib is a supernumerary or accessory rib arising from the seventh cervical vertebra. They occur in ~0.5% of the population, and are more common in females. * represents a persistent ossification of the C7 lateral costal element. During early development, this costal element typically fuse with the transverse process and vertebral body. * failure of this process results a long transverse process or complete rib that can be anteriorly fused with the T1 first rib below * cervical ribs are usually asymptomatic, but can cause thoracic outlet syndrome by compression of the brachial plexus or subclavian vessels.